The present invention relates to an electrophotographic copier, facsimile apparatus, laser printer or similar image forming apparatus and, more particularly, to a cartridge for replenishing a two-ingredient developer to an image forming apparatus, and a replenishing device using the same.
A two-ingredient developer, i.e., a mixture of chargeable carrier particles and chargeable toner particles is extensively used with an image forming apparatus of the kind described. The toner particles deposit on the carrier particles due to frictional charge. When development is repeated with this type of developer, the toner particles are sequentially consumed with the result that the toner concentration and, therefore, image density is sequentially lowered. It has been customary to replenish fresh toner to the developer in an amount corresponding to the consumed toner. On the other hand, the carrier particles have their surfaces covered with a substance for enhancing the frictional charging characteristic. The problem with the carrier is, for example, that the above substance sequentially comes off due to the repeated development and thereby deteriorates the carrier.
In light of the above, Japanese Patent Laid-Open Publication No. 53-22747. for example, teaches a system capable of replenishing a fresh two-ingredient developer to a developing unit while discharging a used developer from the unit, thereby replacing the carrier. In addition, this system is capable of replenishing fresh toner independently of the developer in order to control the toner concentration and to thereby maintain an expected developing ability. For this purpose, the system has exclusive mechanisms for replenishing the developer and the toner, respectively. These mechanisms each include an exclusive container storing the developer or the toner. However, this kind of scheme brings about another problem that the independent containers, each needing an exclusive space, increase the overall size of the developing unit and, therefore, that of the image forming apparatus. In addition, the independent containers limit the design freedom of the image forming apparatus.
Moreover, assume that the containers are laid sideways in order to supply the developer and the toner from the respective containers to the range of the developing unit where a developer exists, as proposed in, for example, Japanese Patent Laid-Open Publication Nos. 59-188671, 60-146265, and 62-6285. Then, the independent containers should be each driven by a respective drive and transmission mechanism, resulting in an increase in the number of parts.